1. Field of the Invention
The present invention relates to vehicular safety devices such as air cushions, belt tighteners, or similar arrangements, and, more particularly, to a control circuit for activating a releasing circuit for the safety device in a more reliable manner.
2. Discussion of the Prior Art
In such a releasing circuit for the safety device as described above, a checking circuit is provided to check for the presence of a defect or malfunction in the releasing circuit. The checking circuit is, in general, designed to continuously supply an electric current from a vehicle battery to an ignition element of the safety device thereby to render the ignition element in an operable condition for checking. For this reason, it is required to reduce the power consumption from the battery to as small a value as possible. It is also assumed that, when the vehicle has been subjected to an accident, the ignition element may not be activated due to its disconnection from the battery. For the purpose of avoiding such a problem, a capacitor is adapted as a back-up power source for supplying a charged voltage therefrom to the ignition element, wherein the capacitor is arranged to be previously charged by the power from the battery. There will, however, occur a lapse of time due to the characteristic of an acceleration sensor prior to supply of the charged voltage from the capacitor to the ignition element. If in this instance a large amount of electric current was supplied to the checking circuit from the capacitor before the lapse of time, the ignition element would not be activated due to an insufficient supply of the charged voltage from the capacitor.